Demo, a 17-year-old conference franchise owned by the technology publisher IDG, has served as the springboard for hit products like the Palm Pilot and the TiVo digital video recorder. In San Diego during the second week of September, 70 start-ups will pay $18,500 each to make a six-minute presentation to a crowd of investors, journalists and others.

To Michael Arrington, the elbow-throwing, supercilious founder of the popular Silicon Valley blog TechCrunch, Demo’s business model amounts to “payola.”